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Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Sat Nov 14, 2015 2:26 pmby Pompeydave
Hi all, just building what I hope is going to be a grunty little Casa 185 engine. For maximum torque should the edge of the piston crown (is that the deck?) be below the bottom of the exhaust port by 1mm? I'm sure I read '1mm below' somewhere, but can't find the info. Any tips appreciated please!
Going to be running it with a PWK 28mm and MB BGM Clubman, and Electrix stator with Kytronic adv/retarder.
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Sat Nov 14, 2015 2:58 pmby mickyb
I believe that the piston should be level with or just above the bottom of he exhaust port at BDC not below as this can cause a heat build up at that point on the piston. No doubt someone who knows better will correct me if I'm wrong
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Sat Nov 14, 2015 6:49 pmby Wack
I would have thought you'll be going the wrong way if the piston is below the exhaust and transfer ports as the timings are longer.
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Mon Nov 16, 2015 7:10 pmby Pompeydave
Ok, many thanks. looks like 1mm above the bottom of the port is the way to go.
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Mon Nov 16, 2015 10:18 pmby Scooterlam
what case are you using, indian, Italian Spanish?
what squish (piston to head) if any, measured around the edge with out head gasket.
Alternatively what's the measurement from the bottom of the exhaust to the top of the barrel and is the head recessed.
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Mon Nov 16, 2015 10:30 pmby Pompeydave
Apologies, should have mentioned the country of origin and squish- Italian GP125 casing with a squish of 1.1mm.
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Mon Nov 16, 2015 10:46 pmby Scooterlam
With or with out base gasket?
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Mon Nov 16, 2015 10:49 pmby Pompeydave
With base gasket. No head gasket- looks like it doesn't use one as the head is recessed to fit more squarely on the barrel.
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Mon Nov 16, 2015 11:24 pmby Scooterlam
1.1mm squish is at the lower end of safe but I,ve run this before with no problems.
My thoughts are that the piston should be flush with bottom of the exhaust port at Bdc. the theory is that the hot gases escaping will hit the wall of the barrel and cause excessive heat. But If my understanding of the 2 stroke is correct by the time the piston is that far down, the exhaust port will effectively be closed or being feed by a fresh charge that has already passed thru the cylinder and is being forced back into the cylinder by the reverse pulse from the chamber.
a rather long winded way of saying, If it were mine I would fit and run.
Re: Casa 185 piston edge (deck?) to Exhaust port height
Posted:
Mon Nov 16, 2015 11:31 pmby Pompeydave
Yep, that's my instinct too. I'll run it as it is and report back. Thanks for the advice
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